Piston for a setting tool

ABSTRACT

A piston for a setting tool which is driven y expanding gases, includes a piston head ( 11 ) and a piston body ( 12 ) connectable along an interface ( 13 ) with the piston head ( 11 ), the piston head ( 11 ) and the piston body ( 12 ) having, respectively, in an interface region, at least one stop surface ( 14 ) and at least one counter-stop surface ( 15 ) formed by surfaces defining essentially complementary tapering regions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piston for a setting tool driven by expanding gases and including a piston head, and a piston body connectable with the piston head along an interface, with the piston head and the piston body having, respectively, in an interface region, at least one stop surface and at least one counter-stop surface.

2. Description of the Prior Art

In the setting tools driven by expanding gases, a piston is displaceably arranged in a piston guide and is driven by expanding gases such as, e.g., combustion gases. The piston head defines a piston area.

In setting tools with a comparatively small drive pressure, the piston area should be significantly increased in order to provide a sufficiently large driving force. In order to prevent the increase of weight by the same amount, the piston body and the piston plate or head are formed as separate parts of different materials and are then assembled. The piston body is formed, preferably, of a high-strength material because it directly contacts the set-in fastening element and should transmit, at a small diameter, large forces.

U.S. Pat. No. 5,860,580 discloses such a two-part piston in which threaded connection provides for a fixed connection of the piston head with the piston body. The necessary centering of the piston head with the piston body is carried out by the thread, whereas the transverse alignment of the piston head with the piston body is carried out by opposite flat or planar surfaces of the piston head and the piston body.

The drawbacks of such a piston consist in that the thread adversely influences the orthogonality because it is subjected to distortion upon hardening of the piston body by heat treatment. The manufacturing of such piston is very expensive.

Accordingly, an object of the invention to provide a piston for a setting tool driven by expanding gases in which the above-discussed drawbacks are eliminated.

SUMMARY OF THE INVENTION

This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a piston in which the stop surface and the counter-stop surface are formed by surfaces defining essentially complementary tapering regions.

The substantially complementary tapering regions insure an orthogonal alignment of the piston body with the piston head. A secondary adjustment or even bending of the piston into a correct position is not any more necessary.

It is beneficial when the complementary tapering regions are formed as cone-shaped regions. The cone-shaped insure a backlash-free connection.

Advantageously, the stop surface, which is provided on the piston head, is formed as an inner cone, and the counter-stop surface, which is provided on the piston body, is formed as a substantially complementary outer cone. Thereby, a geometry, which is easy to produce, is obtained.

Advantageously, the stop surface and the counter-stop surface are inclined to a surface extending parallel to the piston head at an angle α from 10° to 80°.

According to another advantageous embodiment, the complementary tapering regions are formed as spherical regions. The spherical regions likewise insure a backlash-free connection.

Advantageously, the stop surface, which is provided on the piston head is formed as an inner sphere, and the counter-stop surface, which is provided on the piston body, is formed as a substantially complementary outer sphere. Thereby, a geometry, which is likewise easy to produce, is obtained.

It is advantageous when the interface has thread connection elements. The thread connection elements insure that a fixed connection can be easily obtained, which provides for alignment of the piston body when the piston head and the piston body are screwed together.

The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when ready with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show:

FIG. 1 a longitudinal cross-sectional view of a piston according to the present invention; and

FIG. 2 a cross-sectional view of a section of a piston according to another embodiment and corresponding to cut-out II in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a first embodiment of a piston 10 according to the present invention for a setting tool driven by expanding gases. The piston 10 is formed of two parts and has a plate-shaped piston head 11, which extends in a plane 19 transverse to the piston axis 16, and an elongate, extending in the direction of the piston axis 16, piston body 12. The piston head 11 and the piston body 12 are connected with each other along an interface 13. To this end, the interface 13 is provided with thread means consisting of a threaded journal 17 provided on the piston body 12, and a threaded bore 18 formed in the piston head 11. In the piston head 11, there is provided a stop surface 14 that is formed as an inner cone surrounding the mouth of the threaded bore 18. A counter-stop surface 15, which surrounds a shoulder section of the threaded journal 17, abuts the stop surface 14. The counter-stop surface 15 is formed as an outer cone substantially complementary to the inner cone that forms the stop surface 14. The stop surface 14 and the counter-stop surface 15 extend, respectively, in a plane extending parallel to the plane 19. The stop surface 14 and/or the counter-stop surface 15 are inclined at an angle α between 10° and 80° relative to the plane 19 extending parallel to the piston head 11.

During the assembly of the piston 10, the alignment of the piston body 12 relative to the piston head 11 takes place over the conical stop surface 14 and the complementary thereto, conical counter-stop surface 15, without a need in any further adjustment. It should be understood that both the stop surface 14 and the counter-stop surface 15 can be formed as interrupted surfaces.

FIG. 2 shows another embodiment of a piston according to the present invention. The piston 10, which is shown in FIG. 2, differs from the piston 10 shown in FIG. 1 only in that the stop surface 14 and the counter-stop surface 15 are formed as spherical annular surfaces. Here likewise, during the assembly of the piston 10, the alignment of the piston body 12 relative to the piston head 111 takes place over the spherical stop surface 4 and, the complementary thereto, spherical counter-stop surface 15, without a need in any further adjustment.

Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and are not to be construed as a limitation thereof, and various modifications of the present invention will be apparent to those skilled in the art. It is, therefore, not intended that the present invention be limited to disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims. 

1. A piston for a setting tool driven by expanding gases, comprising a piston head (11); and a piston body (12) connectable with the piston head (1) along an interface (13), the piston head (11) and the piston body (12) having, respectively, in an interface region, at least one stop surface (14) and at least one counter-stop surface (15), the stop surface (14) and the counter-stop surface (15) being formed by surfaces defining essentially complementary tapering regions.
 2. A piston according to claim 1, wherein the complementary tapering regions are formed as cone-shaped region.
 3. A piston according to claim 2, wherein the stop surface (14), which is provided on the piston head (11), is formed as an inner cone, and the counter-stop surface (15), which is provided on the piston body (12), is formed as a substantially complementary outer cone.
 4. A piston according to claim 1, wherein the stop surface (14) and the counter-stop surface (15) are inclined to a surface (19) extending parallel to the piston head (11) at an angle (a) from 10° to 80°.
 5. A piston according to claim 3, wherein the complementary tapering regions are formed as spherical regions.
 6. A piston according to claim 5, wherein the stop surface (14), which is provided on the piston head (11) is formed as an inner sphere, and the counter-stop surface (15), which is provided on the piston body (I 2), is formed as a substantially complementary outer sphere.
 7. A piston according to claim 1, wherein the interface (13) comprises thread connection means. 